Pre-occupancy assessments for indoor air quality

Many commercial and public buildings have sat empty over recent months with ventilation systems sitting dormant as the country has been placed in lockdown. The resulting poor air quality may pose a risk to the health of tenants and staff. Pre-occupancy assessments can help protect against this.


Help prevent the spread of COVID-19 in your workplace

As these restrictions are slowly relaxed and places of work are brought back to life, occupiers need to ensure that workplaces have effective ventilation and a sufficient quantity of fresh air to help prevent the spread of COVID-19.

Our Health, Safety and Risk team have put together the following guidance using simple measures that can be implemented ahead of reoccupation, utilising a building’s existing Heating, Ventilation and Air Conditioning (HVAC) system, to ensure a clean, hygienic working atmosphere is available from day one.


Photograph of an empty office block

What should I do? 

Ensure correct ventilation

Ideally ventilation systems should be kept on at all times. Two hours before and two hours after normal working hours the ventilation should be at the normal working speed. Outside of this, fan speed should be reduced but kept on helping to remove any virus particles from the building, including those that may be released from surfaces.

It should be confirmed that toilet area extracts are kept on 24/7 and a negative pressure is maintained.

  • Ensure that if your HVAC system utilises re-circulated air, that this system is bypassed and only 100% fresh air is supplied to the floor.
  • Switching off fan coil units is not necessary as keeping these operational will help to reduce stagnant air pockets.
  • Where there is no HVAC system present, windows should be used to increase fresh air rates much more than normal (accepting though this may cause some thermal discomfort). The exception to this is in the case of mechanically or passive stack extracted toilets, as opening the windows in these areas can allow contaminated air to flow into the rest of the building.

Maintain systems in line with normal procedures

Ductwork cleaning

There is no need to complete any extra disinfection or additional cleaning of the HVAC system in  response to the COVID-19 pandemic. If the above practices are followed, the small particles which the virus is most likely to attach to are unlikely to deposit in the ductwork.  

Changing filters

Filters installed on air intakes are, for operational reasons, typically low to medium efficiency products which are not capable of removing viruses from the air stream. However, this does not mean that they won’t have an effect in removing the virus. In the rare occasions when the outside air is the source of the contamination, a virus is more likely to accumulate on larger particles already trapped on the filter. In this regard increasing the frequency of filter changes could be counterproductive.  

Furthermore, in light of the above it should be assumed that all filters are contaminated (especially any extract filters) so should be changed in line with standard safety procedures. This would include wearing gloves, respiratory protection and disposing the filters in sealed bags.

If you have any questions relating to your individual buildings indoor air quality, please get in touch with a member of our team.

This summary was compiled from the guidance document provided by: REHVA (Federation of European Heating, Ventilation and Air Conditioning Associations) – “REHVA COVID-19 guidance document


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Mike Rose

Divisional Director - Health & Safety T: +44 20 3691 0500 Email
London - Farringdon Street | UK

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